How to Grow Petunias

Annuals for Spring

As a versatile flower, it is hard to go past the petunia. They are prolific bloomers, easy to grow, colourful and have a long flowering season. Petunias are native to Argentina but are now grown virtually around the world. New hybrids and colours mean there is a huge choice of varieties. Petunias are annuals. Single and double flowers are available in striped, veined or solid colours. The petals may be ruffled or smooth and the habit upright or trailing. Some even have a perfume. The flower is wide and trumpet-shaped. The foliage is branching, hairy and slightly sticky.

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Petunias belong to the same family, Solanaceae, as the capsicum, tomato, potato, aubergine, eggplant and tobacco plant.

Most petunias are hybrids. The two oldest types are grandiflora and multiflora. Petunias will flower repeatedly. Some varieties will need deadheading and/or pruning back if they are to continue to set flower buds. Petunias prefer full sun or, if the area is hot, partial shade. Extreme heat will see the plants stop setting flowers for a period. Soil for petunia plants must be freely draining. The Ph is not too critical but adding organic manures will always be beneficial.

The grandiflora have large flowers, either single or double blooms, and are probably the most popular of the four types. The disadvantage with the grandiflora is that it will discolour and collapse if watered from overhead. It is an ideal candidate for container planting if kept out of the rain and watered from below.

Multifloras also come in single and double blooms. They are ideal for planting en masse, creating great swathes of smaller but more abundant flowers than grandiflora and their habit is often more compact. They cope better with rainy conditions.

Millifloras are compact. There is a very profuse flowering of small blooms. They are a good choice for edging purposes and also look great as container plants when mixed with other flowering annuals.

The groundcover or spreading petunia will cover a huge area by the end of the growing season. They look great spilling from hanging baskets, window boxes, over a wall or down a slope. As a rule, they won't need deadheading.

Pinching out the tip of seedlings will encourage a bushier growth. Up to half can be removed if the plant is spindly. Excessive stem growth may be the result of too much water. Organic fertiliser will benefit petunias but overdoing the dose will again result in lavish foliage but few flowers. Good drainage is essential.

If propagating from seed, ten to twelve weeks may elapse before seedlings are strong enough to plant out. Sprinkle seeds on to damp potting mix and pat down lightly. Trays can be placed on heat pads or the top of the refrigerator. Alternatively, cover the tray with clear plastic and place in a warm, light spot. Do not place in direct sunlight. Use a fine mist to water the seeds and remove the plastic as soon as the seedlings emerge. Transplant into pots when the plant has three proper leaves. Do not plant into the garden until there is no danger of frost. To encourage a compact habit and continual blooming, remove spent blooms and lightly prune back long stems.

Petunias may be attacked by aphids and caterpillars. Hose off aphids and use an appropriate powder for caterpillars. If there is grey mould or soft rot in your area, look for resistant varieties.

Petunias have a great reputation and are used in many public areas. Curators of parks, street verges and public gardens appreciate the colour, versatility and easy maintenance of the petunia.